Sample test cards have been used to analyze blood or other biological samples in a spectroscopic or other automated reading machine. Such machines receive a small test card, roughly the size of a playing card, in which biological reagents, nutrients or other material is deposited and sealed, prior to injection of patient samples.
The test card contains the reagents and receives the patient samples in a series of small wells, formed in the card in rows and columns and sealed, typically with tape on both sides. The test cards are filled with patient sample material through fine hydraulic channels formed in the card. The microorganisms in the samples may then be permitted to grow or reactions to proceed, generally over a period of up to a few hours, although the period varies with the type of bacteria or other substance analyzed and sample used.
The current assignee has commercialized instruments for fast, accurate microbial identification, and antimicrobial susceptibility testing (e.g., Vitek® 2 and Vitek® Compact). These instruments include an incubation stations that maintains sample test cards at a precisely controlled temperature to enhance microorganism growth in the individual sample wells. The incubation station includes a rotating carousel that has a plurality of slots for receiving test sample cards. The carousel is vertically mounted and rotates about a horizontal axis. This rotation about the horizontal axis during incubation causes the test card to be rotated through 360° from a normal “upright” card position, through an “inverted” or “upside-down” card position and then back again to an “upright” position. After the incubation, the samples contained in the wells are placed in front of a laser, fluorescent light or other illumination source. The content of the sample in a given well can then be deduced according to readings on the spectrum, intensity or other characteristics of the transmitted or reflected radiation, since the culture of different bacteria or other agents leave distinctive signatures related to turbidity, density, byproducts, coloration, fluorescence and so forth. The instruments for reading the test cards and the incubation carousel are further described in U.S. Pat. Nos. 5,762,873; 5,888,455; 5,965,090; 6,024,921; 6,086,824; 6,136,270; 6,156,565; and 7,601,300, the contents of which are incorporated herein by reference herein.
Despite the general success of test cards in this area, there is an ongoing desire to improve the performance of the cards and readings on their samples. It is for example an advantage to impress more reaction wells in a given card, so that a greater variety of reactions and therefore discrimination of samples can be realized. A given facility may have only one such machine, or be pressed for continuous analysis of samples of many patients, as at a large hospital. Conducting as many identifying reactions on each sample as possible is frequently desirable, yielding greater overall throughput.
It has also been the case that as the total number of reaction wells on a given card has increased, while the card size has remained constant, the wells have necessarily been formed increasingly close together. With the sample wells crowding each other on the card, it has become more likely that the sample contained in one well can travel to the next well, to contaminate the second well. The threat of increased contamination comes into play especially as card well capacity increases above 30 wells.
The current Vitek® 2 disposable product family uses a sample test card containing 64 individual sample wells into which chemicals can be dispensed for the identification and susceptibility testing of microorganisms in the diagnosis of infectious disease. Each of fill channels of the 64 well test card descend to and enter sample wells at an angle, which results in the natural flow of the sample fluid down through the fill channels by gravity, and resistance to small pieces of undissolved material flowing back up into the fluid circuitry. The fluid flow paths thoroughly dispersed over card, including both front and rear surfaces, also result in a longer total linear travel of the flowing fluid than conventional cards. The increased well-to-well distance leads to a reduction in the possibility of inter-well contamination. The average well-to-well distance of fluid flow channels on the 64 well card is to approximately 35 mm, significantly more than the 12 mm or so on many older card designs. The 64 well test card is further described, for example, in U.S. Pat. Nos. 5,609,828; 5,746,980; 5,869,005; 5,932,177; 5,951,952; and USD 414,272, the contents of which are incorporated herein by reference herein.
However, as previously discussed, the incubation carousel employed in the Vitek® 2 and Vitek® compact instruments rotates the test cards through a 360° rotation from a normal “upright” card position, through an “inverted” or “upside-down” card position and then back again to an “upright” position. This rotation of the card can lead to leaking of the sample well contents into the fill channels of prior art cards like the 64 well card where the fill channels descend to and enter sample wells at an angle. In the case of the 64 well card, the potential for well-to-well contamination is still mitigated by the large distance between wells. However, this requirement for longer distances between the wells limits the total number of wells that can fit on a test card of standard size.
In the case of identification, the use of 64 reactions wells tends to be sufficient. However, employing only 64 wells in determining antibiotic susceptibility is limiting. Increasing the number of wells in the card would allow improved performance by using more wells for a single antibiotic test as well as increase the number of antibiotics that could be evaluated in a single card. Accordingly, there is a need to increase the total well capacity in a standard test card while maintaining the reduction in the possibility of inter-well contamination. The novel test cards disclosed herein satisfy this goal without requiring significant changes to instruments designed to read each well during incubation.